Engine equipped with secondary air supply device

ABSTRACT

An engine equipped with a secondary air supply device includes: a fuel tank disposed over a cylinder head for storing fuel of the engine; an exhaust muffler disposed beneath the fuel tank and below the exhaust port in a region lateral of the cylinder head; an exhaust pipe connecting the exhaust port to the exhaust muffler; a secondary air introduction pipe connected to the exhaust pipe for introducing air into the exhaust muffler; and a tailpipe for discharging exhaust gas of the exhaust muffler to the outside, the exhaust muffler and the fuel tank defining therebetween a space, the tailpipe being disposed to meander in the space.

FIELD OF THE INVENTION

The present invention relates to engines equipped with a secondary air supply device that connects an exhaust port of the engine to an exhaust muffler via an exhaust pipe and supplies air (secondary air) to the exhaust pipe.

BACKGROUND OF THE INVENTION

Among examples of the conventionally-known engines equipped with a secondary air supply device are ones in which an exhaust pipe is provided for directing exhaust gas to an exhaust muffler and in which a secondary air introduction pipe is provided in communication with the exhaust pipe so that air (secondary air) is introduced into the exhaust muffler via the secondary air introduction pipe using exhaust pulsation of the engine. By air being introduced into the exhaust muffler via the secondary air introduction pipe like this, an oxidation-reduction reaction (detoxifying reaction) can be caused in exhaust gas by means of a catalyst (catalytic) converter provided within the exhaust muffler.

Further, as a means for efficiently directing air into the exhaust muffler via the secondary air introduction pipe in such engines, it is required that a tailpipe connected to the exhaust muffler be set to a suitable length. By the tailpipe being set to a suitable length like this, it is possible to achieve a sufficient pulsation effect of the engine and thereby efficiently direct air into the exhaust muffler via the secondary air introduction pipe. Exhaust gas within the exhaust muffler is discharged to the outside through the tailpipe.

Further, one example of such engines equipped with a secondary air supply device is disclosed in Japanese Patent No. 2604659 (hereinafter referred to as “JP '659”), in which respective upper portions of a crankcase and a cylinder are positioned at generally the same height, a fuel tank is provided over a crankcase and an exhaust muffler is provided over a cylinder. With the exhaust muffler provided over the cylinder, the exhaust muffler is located at a high position so that a sufficient space is secured beneath the exhaust muffler. The tailpipe is provided to extend downward using the space, so that a suitable length of the tailpipe can be secured.

The engine equipped with a secondary air supply device disclosed in JP '659 is used, for example, in a power generator. In the case where such an engine is used in a power generator, the engine tends to be driven for a long time, and thus, it is necessary to secure a large storage capacity of the fuel tank. Therefore, in the case where the engine of a small size is used in a power generator, it is conceivable to secure a large storage capacity of the fuel tank by providing the fuel tank over both of the crankcase and the cylinder.

With the fuel tank provided over both of the crankcase and the cylinder as noted above, however, it is difficult to provide the exhaust muffler over the cylinder. To avoid such a difficulty, it is conceivable to provide the exhaust muffler laterally of the cylinder. In the case where the exhaust muffler is disposed laterally of the cylinder, the exhaust muffler is located at a low position. Therefore, it is difficult to secure a space sufficient to allow the tailpipe to extend beneath the exhaust muffler, so that the tailpipe cannot extend downward so as to have a sufficient length.

SUMMARY OF THE INVENTION

In view of the foregoing problems, it is an object of the present invention to provide an improved engine equipped with a secondary air supply device which can secure a sufficient length of the tailpipe without extending the tailpipe in a downward direction.

In order to accomplish the above-mentioned object, the present invention provides an improve engine equipped with a secondary air supply device where an exhaust port for discharging exhaust gas of the engine to outside is formed in a cylinder head, which comprises: a fuel tank disposed over the cylinder head for storing fuel of the engine; an exhaust muffler disposed beneath the fuel tank and below the exhaust port in a region lateral of the cylinder head; an exhaust pipe connecting the exhaust port to the exhaust muffler; a secondary air introduction pipe connected to the exhaust pipe for introducing air into the exhaust muffler; and a tailpipe for discharging exhaust gas of the exhaust muffler to the outside, the exhaust muffler and the fuel tank defining therebetween a space, the tailpipe being disposed to meander in the space.

According to the present invention, the exhaust muffler is disposed beneath the fuel tank, and the space is defined between the exhaust muffler and the fuel tank. Further, the tailpipe, through which exhaust gas of the exhaust muffler is discharged to the outside, is disposed in a meandering configuration in the space. The tailpipe disposed in such a meandering configuration in the space can have a suitable length in the limited space without extending downward.

In a referred implementation, the exhaust pipe is connected to the exhaust port by means of a fastener member, and the tailpipe meanders in the space in such a manner as to avoid an imaginary extension line of the fastener member.

In the case where the exhaust muffler is disposed beneath the fuel tank and below the exhaust port in a region lateral of the cylinder head and where the exhaust pipe is connected to the exhaust port by means of the fastener member as noted above, the fastener member is located in the space between the exhaust muffler and the fuel tank. Thus, sometimes, it is likely that the tailpipe disposed in the space is located on the imaginary extension line of the fastener member. If the tailpipe is located on the imaginary extension line of the fastener member, operations for attaching and detaching the fastener member might be undesirably disturbed by the existence of the tailpipe, and the tailpipe might interfere with the fastener member. To avoid such an inconvenience, the tailpipe in the preferred implementation of the present invention is meandered in such a manner as to avoid the imaginary extension line of the fastener member. Thus, the operations for attaching and detaching the fastener member can be performed without being disturbed by the existence of the tailpipe. Further, the tailpipe disposed in such a manner as to avoid the imaginary extension line of the fastener member can be prevented from interfering with (hitting) the fastener member, which can secure an enhanced durability of the tailpipe.

The following will describe embodiments of the present invention, but it should be appreciated that the present invention is not limited to the described embodiments and various modifications of the invention are possible without departing from the basic principles. The scope of the present invention is therefore to be determined solely by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain preferred embodiments of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a front view showing a power generator employing an embodiment of an engine equipped with a secondary air supply device of the present invention;

FIG. 2 is a view taken in the direction of arrow 2 of FIG. 1;

FIG. 3 is a perspective view showing an exhaust means provided in the engine and the secondary air supply device of FIG. 1;

FIG. 4 is an exploded perspective view corresponding to FIG. 3;

FIG. 5 is an enlarged view of a section surrounded at 5 in FIG. 1;

FIG. 6 is a perspective view showing the secondary air supply device of FIG. 3;

FIG. 7 is an exploded perspective view of the secondary air supply device of FIG. 6;

FIG. 8 is a perspective view of the secondary air supply device of FIG. 6 taken from the side of a filter cover;

FIG. 9 is an exploded perspective view of the filter cover and an intake nozzle of FIG. 7; and

FIGS. 10A and 10B are views illustrative of how exhaust gas is oxidized or reduced by the embodiment of the engine equipped with the secondary air supply device, dust, dirt etc. are prevented from entering the intake nozzle and fuel is prevented from adhering to the intake nozzle.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a front view showing a power generator 10 employing an embodiment of an engine 12 equipped with a secondary air supply device 26 of the present invention. For ease of understanding of a construction of the embodiment, let it be assumed that, in FIG. 1, directions toward and away from a reader of the figure are “forward” and “rearward”, respectively, and left and right sides of the figure are “one side” and “other side”, respectively.

As shown in FIG. 1, the power generator 10 includes the engine 12 equipped with the secondary air supply device 26, a power generation section 14 provided integrally on the engine 12, a fuel tank 16 for storing fuel to be supplied to the engine 12, and a frame 18 supporting the power generator 10.

The power generation section 14 is provided on one side portion (left side portion in FIG. 1) 31 a of the engine 12 (more specifically, one side portion 31 a of a crankcase 31), and the fuel tank 16 is provided over respective upper portions 12 a and 14 a of the engine 12 and the power generator 10. With the fuel tank 16 provided over the engine 12 and the power generator 10 like this, a large storage capacity of the fuel tank 16 can be secured.

The engine 12 is a power-generating general-purpose internal combustion engine which includes: an engine body 21; a cooling fan 22 provided integrally on the engine body 21; a carburetor 23 provided in communication with an intake port of the engine body 21; an air cleaner 24 provided in communication with the carburetor 23; an exhaust means 25 provided in an exhaust port 42 (FIG. 2) of the engine body 21; and the secondary air supply device (AI: Air Injection) 26 provided in communication with the exhaust means 25.

The engine body 21 includes the crankcase 31, a cylinder block 32 formed integrally with the crankcase 31, a cylinder head 33 provided on the cylinder block 32, and a head cover 34 covering the cylinder head 33. The cylinder block 32 will hereinafter be referred to also as “cylinder”, for convenience of description. The cylinder 32 extends obliquely from the crankcase 31 so that a lower space 36 is defined beneath the cylinder 32, and the fuel tank 16 is disposed over the cylinder head 33.

The cooling fan 22 is located adjacent to respective side portions of the crankcase 31 and the cylinder head 33 by being provided on the other side portion 31 b of the crankcase 31. A recoil starter is connected to the cooling fan 22, so that impellers of the cooling fan 22 rotate by a human operator pulling a handle 38 of the recoil starter and rotation of the impellers is transmitted to a crankshaft. Thus, the crankshaft rotates, so that the engine 12 is driven. By the engine 12 being driven like this, the power generation section 14 is driven.

The carburetor 23 is located closer to the lower space 36 than the cooling fan 22 and communicates with the intake port of the cylinder head 33. The air cleaner 24 is provided in communication with the carburetor 23. An inlet 24 a of the air cleaner 24 is located beneath the carburetor 23.

Air is directed through the intake 24 a of the air cleaner 24 into the air cleaner 24, so that fuel is vaporized by the carburetor 23 and the thus-vaporized fuel is directed to the cylinder head 33 via the intake port.

A discharge pipe 39 is provided in communication with a lower portion 23 a of the carburetor 23. Thus, the fuel directed to the carburetor 23 is discharged to the outside 61 via the discharge pipe 39 as it drops from the lower portion 23 a of the carburetor 23.

The exhaust means 25 includes an exhaust muffler 41 disposed adjacent to the one side (left side in FIG. 1), an exhaust pipe 43 connecting the exhaust port 42 (FIG. 2) to the exhaust muffler 41, and a tailpipe 44 that discharges exhaust gas of the exhaust muffler 41 to the outside 61. The exhaust port 42 is formed in the one side portion (left side portion in FIG. 1) 33 a of the cylinder head 33, so that exhaust gas within the cylinder 32 is discharged to outside of the cylinder head 33 via the exhaust port 42.

Further, the power generation section 14 and the exhaust muffler 41 are disposed opposite from the carburetor 23 with the cylinder 32 and the cylinder head 33 interposed therebetween. The exhaust muffler 41 is disposed forward (in front) of the power generation section 14.

Further, a partition member 46 is fixed to the engine 12 and the power generation section 14 by means of a bolt 47. The exhaust muffler 41 is partitioned off from the fuel tank 16 via an upper wall portion 46 a of the partition member 46. Further, the exhaust muffler 41 is partitioned off from the engine 12 via a side wall portion 46 b of the partition member 46.

Further, as shown in FIGS. 2 and 3, the exhaust muffler 41 is disposed beneath the fuel tank 16 and below the exhaust port 42. The exhaust muffler 41 has a retaining cylinder 53 accommodated in the interior 52 of the muffler box 51, and a catalyst converter 54 retained on the inner wall of the retaining cylinder 53.

A muffler box 51 is in the form of a hollow box of a rectangular parallelepiped shape. The fuel tank 16 is disposed beneath the fuel tank 16 by being fixed, for example, to a boss 15 of the power generation section 14 by means of a bolt 55. Thus, the fuel tank 16 is located above an upper muffler surface portion 51 a of the muffler box 51, so that an upper space 56 is defined between the upper muffler surface portion 51 a and a lower portion 16 a of the fuel tank 16.

The retaining cylinder 53 has a front end portion 53 a communicating with the interior of the cylinder head 33 (more specifically, a combustion chamber) via the exhaust pipe 43 and the exhaust pipe 42. Further, a rear end portion 53 b of the retaining cylinder 53 has a rear opening portion (not shown) that opens to the interior 52 of the muffler box 51.

Further, as shown in FIG. 4, the exhaust pipe 43 has a flange 57 formed on its front end portion 43 a and connected to the one side portion (left side portion) 33 a of the cylinder head 33 by means of a bolt 58 and a nut 59 (see also FIG. 2). Thus, the front end portion 53 a of the exhaust pipe 43 communicates with the exhaust port 42 of the cylinder head 33. Also, the exhaust pipe 43 has a rear end portion 43 b communicating with the front end portion 53 a of the retaining cylinder 53.

Thus, exhaust gas within the cylinder 32 is directed to the exhaust port 42, the exhaust pipe 43 and to the retaining cylinder 53. The exhaust gas thus directed to the retaining cylinder 53 is subjected to oxidation-reduction (detoxification) by the catalyst converter 54 within the retaining cylinder 53. The exhaust gas having been thus subjected to oxidation-reduction by the catalyst converter 54 is directed through the rear opening portion of the retaining cylinder 53 to the interior 52 of the muffler box 51.

The tailpipe 44 has a proximal end portion 44 a connected to a front wall 51 b of the muffler box 51 so that it communicates with the interior 52 of the muffler box 51. Further, the tailpipe 44 has a distal end portion 44 b opening to the outside 61 of the muffler box 51. Although the tailpipe 44 comprises a plurality of interconnected pipes as shown in the figures, it will hereinafter be described as comprising a single bent pipe, for convenience of description.

In the illustrated example, the tailpipe 44 comprises a first pipe section 63, a second pipe section 64, a third pipe section 65, a fourth pipe section 66 and a fifth pipe section 67. The tailpipe 44 is bent so that the first to fifth pipe sections 63 to 67 are interconnected in a meandering configuration.

Referring back to FIG. 2, the first pipe section 63 is connected at the proximal end portion 44 a to the front wall 51 b of the muffler box 51 and extends obliquely forward and upward away from the front wall 51 b. The first pipe section 63 has a front end portion 63 a located near the upper muffler surface portion 51 a of the muffler box 51.

The second pipe section 64 extends upward from the front end portion 63 a of the first pipe section 63 in an arcuately curved shape. Because the front end portion 63 a of the first pipe section 63 is located near the upper muffler surface portion 51 a of the muffler box 51, the second pipe section 64 is located in the upper space 56 higher than the upper muffler surface portion 51 a.

The third pipe section 65 extends substantially horizontally from an upper end portion 64 a of the second pipe section 64, toward the power generator 14 (i.e., rearward), to a rear end portion 51 c of the upper muffler surface portion 51 a. Thus, the third pipe section 65 is located in the upper space 56 higher than the upper muffler surface portion 51 a.

Further, as shown in FIG. 4, the fourth pipe section 66 extends substantially horizontally from a rear end portion 65 a of the third pipe section 65, toward the cylinder head 33 (i.e., toward the one side portion), to near an end portion 51 d of the upper muffler surface portion 51 a (see also FIG. 1). Thus, the fourth pipe section 66 is located in the upper space 56 higher than the upper muffler surface portion 51 a. Further, the fourth pipe section 66 has an end portion 66 a located above the end portion 51 d of the upper muffler surface portion 51 a. A first horizontally curved portion 68 is formed in an intersecting portion between the rear end portion 65 a of the third pipe section 65 and another end portion 66 b of the fourth pipe section 66.

Further, the fifth pipe section 67 extends substantially horizontally forward from the end portion 66 a of the fourth pipe section 66. Thus, the fifth pipe section 67 is located in the upper space 56 higher than the upper muffler surface portion 51 a and the exhaust pipe 43. An outer cylinder 71 is provided around the outer periphery of the fifth pipe section 67, and the outer cylinder 71 is supported on an upper end portion 72 a of a support member 72. The support member 72 is fixed at its lower end portion 72 b to the front wall 51 b of the muffler box 51.

A distal end portion 44 b of the fifth pipe section 67 (i.e., distal end portion of the tailpipe 44) projects forward beyond a front end portion 51 e of the upper muffler surface portion 51 a. A second horizontally curved portion 69 is formed in an intersecting portion between the end portion 66 a of the fourth pipe section 66 and a rear end portion 67 a of the fifth pipe section 67.

Here, the fifth pipe section 67 is spaced apart from the bolt 58 and the nut 59 fastening the flange 57 to the cylinder head 33; more specifically, the fifth pipe section 67 is located closer to the one side portion 31 a than the bolt 58 and the nut 59. Further, with the second to fifth pipe sections 64 to 67 located above the upper muffler surface portion 51 a, these pipe sections 64 to 67 are disposed in the upper space 56 (see FIG. 2).

Further, as shown in FIGS. 2 and 4, the tailpipe 44 is formed in such a manner that the first to third pipe sections 63 to 65 meander in a generally V shape as viewed laterally from one side of the muffler 41 (i.e., as viewed in a horizontal direction). Further, the tailpipe 44 is disposed in such a manner that the third to fifth pipe sections 65 to 67 meander in the upper space 56 in a generally U shape as viewed in the vertical direction.

Namely, the whole of the tailpipe 44 (more specifically, the second to fifth pipe sections 64 to 67 of the tailpipe 44) is formed in the upper space 56 so as to meander in the horizontal and vertical direction. By meandering in the upper space 56, the tailpipe 44 can have a suitable length in the limited upper space 56 without extending downward.

Further, the third to fifth pipe sections 65, 66 and 67 are located above and forward of an imaginary horizontal extension line 74 extending from the axis of the bolt 58 and the nut 59 while avoiding the imaginary extension line 74. Namely, the entire tailpipe 44 is provided to meander in the space 56 while avoiding the imaginary extension line 74.

The following explain in detail why the entire tailpipe 44 is provided to meander in such a manner as to avoid the imaginary extension line 74. Namely, the exhaust muffler 41 is disposed beneath the fuel tank 16 and below the exhaust port 42 in a region lateral of the one side of the cylinder head 33. Further, the exhaust pipe 43 is fixedly connected to the one side portion 33 a of the cylinder head 33 by means of the bolt 58 and the nut 59, and the exhaust pipe 43 communicates with the exhaust port 42. Thus, the bolt 58 and the nut 59 are located in the upper space 56 between the exhaust muffler 41 and the fuel tank 16.

Therefore, in some cases, it is conceivable that the tailpipe 44 disposed in the upper space 56 is located on the imaginary extension line 74 of the bolt 58 and the nut 59, in which cases operations for attaching and detaching the bolt 58 and the nut 59 might be undesirably disturbed by the existence of the tailpipe 44.

Thus, in the instant embodiment, the third to fifth pipe sections 65 to 67 of the tailpipe 44 are disposed above and forward of the imaginary extension line 74 so as to avoid the imaginary extension line 74. In this way, the entire tailpipe 44 can be meandered in such a manner as to avoid the imaginary extension line 74, and thus, the bolt 58 and the nut 59 can be attached and detached without being disturbed by the existence of the tailpipe 44.

In addition, the tailpipe 44 (more specifically, the fifth pipe section 67) is spaced apart from, i.e. disposed closer to the one side portion than, the bolt 58 and the nut 59. In this way, the tailpipe 44 can be prevented from interfering with (hitting) the bolt 58 and the nut 59 and thus can have a sufficient durability.

Further, the proximal end portion 44 a of the tailpipe 44 is in communication with the interior 52 of the muffler box 51, and the distal end portion 44 b of the tailpipe 44 opens to the outside 61. Thus, exhaust gas directed to the interior 52 of the muffler box 51 through the rear opening portion of the retaining cylinder 53 is discharged to the outside 61 of the muffler box 51 via the tailpipe 44. The secondary air supply device 26 is in communication with the exhaust pipe 43 of the exhaust means 25.

Further, as shown in FIG. 5, the secondary air supply device 26 includes: a secondary air introduction pipe 81 connected to the exhaust pipe 43 (see FIG. 1); a one-directional valve 82 provided on the secondary air introduction pipe 81; an air filter 83 connected to the one-directional valve 82; an intake nozzle 84 connected to the air filter 83; and a partition wall 85 supporting the intake nozzle 84.

Further, as shown in FIG. 3, the secondary air introduction pipe 81 has an outlet end portion 81 a connected to a portion of the exhaust pipe 43 adjacent to the flange 57. The secondary air introduction pipe 81 is meandered in the upper space 56 and extends in a downward slope from the upper space 56 to the lower space 36 (see also FIG. 1), so that an inlet end portion 81 b of the secondary air introduction pipe 81 is located in the lower space 36. With the secondary air introduction pipe 81 meandered in the upper space 56 and extending in a downward slope from the upper space 56 to the lower space 36 as noted above, a suitable length of the secondary air introduction pipe 81 can be secured.

Further, as shown in FIG. 6, an outlet pipe 86 of the one-directional valve 82 is connected via a connection pipe 87 to the inlet end portion 81 b of the secondary air introduction pipe 81. The one-directional valve 82 is opened in response to pressure in the interior 52 (see FIG. 3) of the muffler box 51 becoming negative due to exhaust pulsation of the engine 12, and the one-directional valve 82 is closed in response to the pressure in the interior 52 of the muffler box 51 becoming positive due to the exhaust pulsation of the engine 12. Thus, once the pressure in the interior 52 of the muffler box 51 becoming negative, air (secondary air) can be introduced into the secondary air introduction pipe 81 via the one-directional valve 82. The air filter 83 is provided upstream of the one-directional valve 82.

Further, as shown in FIG. 7, the air filter 83 includes: a filter case 93 fixed to a boss 13 of the engine 12 by means of a bolt 91; a filter (not shown) accommodated in the filter case 93; and a filter cover 95 fixed to an opening portion 93 a of the filter case 93 by means of a bolt 94. Air is sucked into the air filter 83 from the intake nozzle 84. The air thus sucked into the air filter 83 is filtered through the filter and then introduced into the secondary air introduction pipe 81 via the one-directional valve 82.

Further, as shown in FIG. 8, a filter inlet pipe 96 extends in a curved shape from a front wall 95 a of the filter cover 95 toward an upper inlet, and an inlet port 96 a of the filter inlet pipe 96 projects vertically upward. An outlet port 96 b (see FIG. 7) of the filter inlet pipe 96 is located within the air filter 83 opens toward the upstream end of the filter. A fitting nozzle section 84 a of the intake nozzle 84 is fittingly connected to the inlet port 96 a of the filter inlet pipe 96.

Further, as shown in FIG. 9, the intake nozzle 84 includes the fitting nozzle section 84 a extending vertically to be fitted over the inlet port 96 a of the filter inlet pipe 96, and an extension nozzle section 84 c extending from an upper end portion 84 b of the fitting nozzle section 84 a in a direction opposite from (i.e., away from) the cooling fan 22 (see FIG. 1). With the fitting nozzle section 84 a and the extension nozzle section 84 c, the intake nozzle 84 is formed in a generally inverted-J shape.

The extension nozzle section 84 c has its distal end portion 84 d inserted in a through-hole 88 of the partition wall 85. With the fitting nozzle section 84 a fitted over the inlet port 96 a of the filter inlet pipe 96 and the distal end portion 84 d inserted in the through-hole 88 as noted above, the intake nozzle 84 is fixed to the inlet port 96 a and the partition wall 85.

Referring now back to FIG. 5, with the intake nozzle 84 fixed in the aforementioned manner, an opening portion 84 e of the intake nozzle 84 opens in the opposite direction from the cooling fan 22 (see FIG. 1). Further, the opening portion 84 e of the intake nozzle 84 is located beneath the carburetor 23 and closer to the one side portion (i.e., closer to the lower space 36) than the carburetor 23.

Further, as shown in FIG. 3, the intake nozzle 84 is in communication with the secondary air introduction pipe 81 via the air filter 83 and the one-directional valve 82. Thus, air sucked in through the opening portion 84 e of the intake nozzle 84 by the exhaust pulsation of the engine 12 is directed to the secondary air introduction pipe 81 via the intake nozzle 84, the filter inlet pipe 96, the air filter 83 and the one-directional valve 82.

Further, the air directed to the secondary air introduction pipe 81 as noted above is directed into the retaining cylinder 53 of the exhaust muffler 41 via the secondary air introduction pipe 81 and the exhaust valve 43. Thus, the air sucked in through the opening portion 84 e of the intake nozzle 84 is directed to the catalyst converter 54 of the retaining cylinder 53.

Further, as shown in FIGS. 5 and 9, the partition wall 85 projects upward from an upper portion 95 b of the filter cover 95, and the through-hole 88 is formed through the thickness of the partition wall 85. Thus, the through-hole 88 is located above the filter cover 95 and an outlet 39 a of the discharge pipe 39. The partition wall 85 is located beneath the carburetor 23 and closer to the one side (i.e., closer to the lower space 36) than the carburetor 23. With the extension nozzle section 84 c inserted through the through-hole 88 of the partition wall 85, the opening portion 84 e of the intake nozzle 83 is located adjacent to a side of the partition wall 85 opposite from the carburetor 23, i.e. the partition wall 85 is located between the opening portion 84 e of the intake nozzle 84 and the carburetor 23.

Further, with the extension nozzle section 84 c inserted through the through-hole 88 of the partition wall 85, the opening portion 84 e of the intake nozzle 84 is located adjacent to a side of the partition wall 85 opposite from the carburetor 23. Namely, the opening portion 84 e of the intake nozzle 84 is partitioned off from the carburetor 23 by the partition wall 85.

The carburetor 23 is located closer to the lower space 36 than the cooling fan 22 (FIG. 1). Thus, the partition wall 85 is located between the opening portion 84 e of the intake nozzle 84 and the cooling fan 22 with the opening portion 84 e partitioned off from the carburetor 23 by the partition wall 85.

Thus, the partition wall 85 can not only prevent cooling air of the cooling fan 22 from reaching the opening portion 84 e but also prevent dust, dirt, rain water, etc. from entering through the opening portion 84 e. Further, the opening portion 84 e opens in the opposite direction from the cooling fan 22, so that it is possible to further reliably prevent dust, dirt, rain water, etc. from entering the intake nozzle 84 through the opening portion 84 e due to cooling air blown from the cooling fan 22.

In some cases, it is conceivable to form, in a wall portion of the air filter 83 closer to the cooling fan 22, an intake inlet for sucking secondary air into the air filter 83. It is also likely for fuel within the carburetor 23 to be dropped (discharged) to the outside 61 via the discharge pipe 39 of the carburetor 23. The discharge pipe 39 is located closer to the lower space 36 than the cooling fan 22, and the intake inlet of the air filter 83 is located closer to the lower space 36 than the discharge pipe 39. Thus, the fuel discharged to the outside 61 via the discharge pipe 39 may undesirably adhere to the intake inlet of the air filter 83 due to cooling air blown from the cooling fan 22.

To avoid such an inconvenience, the extension nozzle section 84 c in the instant embodiment is inserted through the through-hole 88 formed above the filter cover 95 so that the opening portion 84 e of the intake nozzle 84 is located at a position H1 higher than the outlet 39 a of the discharge pipe 39. Further, the partition wall 85 is located between the opening portion 84 e of the intake nozzle 84 and the carburetor 23, and thus, the opening portion 84 e of the intake nozzle 84 is partitioned off from the carburetor 23 by the partition wall 85.

Thus, the partition wall 85 in the instant embodiment can prevent fuel, having been dropped or discharged from the outlet 39 a of the discharge pipe 39, from being directed to the opening portion 84 e and adhering to the opening portion 84 e due to the cooling air from the cooling fan 2.

In addition, the opening portion 84 e of the intake nozzle 84 opens in the opposite direction from the carburetor 23 (outlet 39 a of the discharge pipe 39). Thus, fuel discharged from the outlet 39 a of the discharge pipe 39 can be more reliably prevented from adhering to the opening portion 84 e due to cooling air sent from the cooling fan 22.

Further, because the opening portion 84 e of the intake nozzle 84 is located at the high position H1 above the filter cover 95, it is located higher than the intake 24 a of the air cleaner 24 communicating with the carburetor 23. Thus, in a rainstorm, for example, a water surface will reach the intake 24 a of the air cleaner 24 before reaching the opening portion 84 e of the intake nozzle 84. The engine 12 can be deactivated by the water being sucked in through the intake 24 a of the air cleaner 24, so that the water can be prevented from sucking in through the opening portion 84 e of the intake nozzle 84.

Further, with the intake nozzle 84 connected to the air filter 83, the interior space of the air filter 83 can be used as a resonator, so that a silencing effect can be achieved. In addition, because the opening portion 84 e of the intake nozzle 84 is oriented toward the lower space 36, it is oriented toward the interior of the power generator 10. Thus, sound noise can be effectively prevented from being leaked to the outside, so that a further silencing effect can be achieved.

The following describe, with reference to FIG. 10, an example manner in which exhaust gas is oxidized and reduced by the catalyst converter 54 and entry of dust, dirt, rainwater, etc. into the intake nozzle 84 and adherence of fuel to the intake nozzle 84 is prevented in the instant embodiment.

During driving of the engine 12, as shown in FIG. 10A, exhaust gas is discharged from the distal end portion 44 b of the tailpipe 44 to the outside 61 through the exhaust muffler 41 and the tailpipe 44. At the same time, air (secondary air) is sucked in through the intake nozzle 84 of the secondary air supply device 26 by use of exhaust pulsation of the engine 12, as indicated by arrow A. The air sucked into the intake nozzle 84 is directed to the exhaust pipe 43 via the air filter 83, the one-directional valve 82 and the secondary air introduction pipe 81, as indicated by arrow B.

Further, as shown in FIG. 10B, the air directed to the exhaust pipe 43 is directed through the exhaust pipe 43 to the retaining cylinder 53 together with exhaust gas directed to the exhaust pipe 43, as indicated by arrow C.

Further, in the instant embodiment, it is possible to secure suitable lengths of the tailpipe 44 of the exhaust muffler 41 and the secondary air introduction pipe 81. Thus, by the negative pressure produced by the exhaust pulsation of the engine 12, the air (secondary air) can be reliably supplied to the retaining cylinder 53 (i.e., to the catalyst converter 54).

Thus, the catalyst converter 54 is activated so that exhaust gas directed to the retaining cylinder 53 can be effectively oxidized or reduced (i.e., detoxified). The exhaust gas oxidized or reduced by the catalyst converter 54 is directed from the rear opening portion of the retaining cylinder 53 to the interior 52 of the muffler box 51 as indicated by arrow D. The exhaust gas thus directed to the interior 52 of the muffler box 51 is directed through the tailpipe 44 and discharged from the distal end portion 44 b to the outside 61 as indicated by arrow E.

Referring now back to FIG. 10A, the cooling fan 22 rotates during driving of the engine 12, so that cooling air is sent or blown from the cooling fan 22 toward the engine body 21 as indicated by arrow F. The cooling air thus blown from cooling fan 22 is directed toward the exhaust muffler 41 by way of the lower space 36 as indicated by arrow G.

Because the opening portion 84 a of the intake nozzle 84 is oriented in the opposite direction from the cooling fan 22 and is partitioned off from the carburetor 23 by the partition wall 85, cooling air from the cooling fan 22 can be prevented from reaching the opening portion 84 a. Thus, it is possible to reliably prevent dust, dirt, rain water, etc. from entering through the opening portion 84 e due to cooling air of the cooling fan 22.

Further, the opening portion 84 a of the intake nozzle 84 is located above the outlet 39 a of the discharge pipe 39. In addition, the opening portion 84 a of the intake nozzle 84 is oriented in the opposite direction from the carburetor 23 and partitioned off from the carburetor 23 by the partition wall 85. Thus, fuel having dropped from the outlet 39 a of the discharge pipe 39 can be prevented by the partition wall 85 from being directed to the opening portion 84 e due to cooling air from the cooling fan 22. Thus, the fuel having dropped from the carburetor 23 can be prevented from adhering to the opening portion 84 e of the intake nozzle 84.

It should be appreciated that the engine 12 equipped with secondary air supply device 26 of the present invention is not limited to the above-described embodiment and may be modified variously. For example, whereas the embodiment has been described above in relation to the case where the bolt 58 and the nut 59 are used as fastener members, the bolt 58 and the nut 59 may be replaced with a river or any other suitable fastener member.

Further, the shapes and constructions of the power generator 10, engine 12, fuel tank 16, secondary air supply device 26, cylinder 32, cylinder head 33, exhaust muffler 41, exhaust port 42, exhaust pipe 43, tailpipe 44, bolt 58, nut 59, secondary air introduction pipe 81, etc. are not limited to the ones illustratively shown and described above and may be modified as necessary.

The basic principles of the present invention are well suited for application to engines equipped with a secondary air supply device that connects an exhaust port of the engine to an exhaust muffler via an exhaust pipe and supplies air (secondary air) to the exhaust pipe. 

What is claimed is:
 1. An engine equipped with a secondary air supply device where an exhaust port for discharging exhaust gas of the engine to outside is formed in a cylinder head, the engine comprising: a fuel tank disposed over the cylinder head for storing fuel of the engine; an exhaust muffler disposed beneath the fuel tank and below the exhaust port in a region lateral of the cylinder head; an exhaust pipe connecting the exhaust port to the exhaust muffler; a secondary air introduction pipe connected to the exhaust pipe for introducing air into the exhaust muffler; and a tailpipe for discharging exhaust gas of the exhaust muffler to the outside, the exhaust muffler and the fuel tank defining therebetween a space, the tailpipe being disposed to meander in the space.
 2. The engine according to claim 1, wherein the exhaust pipe is connected to the exhaust port by means of a fastener member, and the tailpipe meanders in the space in such a manner as to avoid an imaginary extension line of the fastener member. 